Recently, in accordance with advances in laser oscillators and the like, a high-power laser is applied to mass production lines such as in cutting and welding of metal. Processing quality of laser processing is greatly influenced by processing parameters such as laser power, laser power density distribution (mode), and processing assist gas. Particularly, appropriate setting of the laser power is an indispensable element in order to obtain favorable processing quality, and thus, a laser power meter having high accuracy is essential.
Generally, a laser power meter of the kW class performs measurement by extracting a portion of a laser beam using attenuation means for attenuating intensity of a laser beam (a partial transmission mirror and the like). However, in this case, since the attenuation means and an optical sensor receiving high power are thermally deteriorated, correction or replacement is necessary substantially every year. This method is often used as a monitor for power in the laser oscillator to control power feedback.
Normally, in order to properly measure laser power, a laser receiving body is irradiated with all the laser beams, the laser beams are converted into heat, and the heat quantity thereof is measured. However, in this method, it takes time for stabilizing the temperatures of the laser receiving body and a coolant. In addition, the measurement cannot be performed when a laser is in use, and thus, this method cannot be used to control the feedback.
A laser receiving unit of the laser power meter disclosed in PTL 1 is formed to have a laser receiving body, a casing, and a cooling channel provided at a position between both thereof. The coolant is supplied to the cooling channel from a water supply apparatus via a pipe. A measurement unit of the laser power meter is configured to include a water meter of the coolant on an entrance side, a water temperature meter such as a thermocouple, and another water temperature meter on an exit side. Using a flow rate Q of the coolant, a water temperature Ti on the entrance side, and another water temperature To on the exit side measured by these instruments, the heat quantity transmitted from a laser receiving portion to the coolant is calculated, thereby obtaining a laser power value. Such a water cooling power damper-type laser power meter can measure power even in a high-power laser up to several tens of kW, thereby being widely used as a power meter of a carbon dioxide laser.